zephyr: turn off I2C
zephyr: turn off I2C

Upstream Zephyr is making a habit of enabling subsystems on any board
that supports them. That's a potential security risk if any of those
allow interference with the running bootloader, and is currently
exceeding mcuboot's flash allowance on some STM32 targets,
e.g. 96b_carbon. Turn off I2C to restore the build for those.

Signed-off-by: Marti Bolivar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@linaro.org>

runtimeco/mcuboot,utzig/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,utzig/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,tamban01/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,utzig/mcuboot,utzig/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,utzig/mcuboot,runtimeco/mcuboot